The type-E coupler is the standard coupler for railway freight cars. As the standard coupler, all producers of such couplers in the United States are required to produce the couplers to a standard specification. Also, a coupler may be reconditioned to extend its useful life. Whether produced originally or reconditioned, couplers must meet certain specifications to ensure that they are completely interchangeable regardless of the manufacturer. In addition, couplers from any manufacturer should be able to be readily joined with couplers from any other domestic manufacturer.
The Association of American Railroads (“AAR”) has adopted standards for railway couplers. The coupler must include specific geometry and dimensions that allow it to receive a knuckle, and the geometry must be such that the knuckle is allowed to freely operate when coupling and uncoupling railway cars. These dimensions and features of the coupler may be checked for compliance with AAR standards by using gauges. When gauges are applied to a coupler in a prescribed manner, it may be verified that certain dimensions of the coupler fall within an allowable variation or tolerance range.